Alpha-methyl-p-bromo-styrene and method of preparation

ABSTRACT

Alpha-methyl-p-bromo-styrene prepared by the manipulative steps of brominating poly(α-methyl-styrene) and subsequently depolymerizing the brominated polymer. The alpha-methyl-p-bromo-styrene has particular utility as a co-monomer for preparing copolymers exhibiting a flame retardancy.

This is a division of application Ser. No. 475,711, filed June 3, 1974,now U.S. Pat. No. 3,959,398.

This invention relates to a bromine containing hydrocarbon, to itsmethod of preparation, and to its copolymer with other reactivematerials. This invention particularly relates to a fire retardancyconveying compound and to its incorporation into polymers.

Fire retardancy is becoming an increasingly desired property of variouspolymers. Many polymeric compositions which presently have acceptableflammability limits may not be acceptable at future times. Therefore,improved methods of imparting flame retardants to polymeric materials iscontinually sought.

Generally, the flammability of organic polymers has been reduced by theaddition of inorganic materials, organometallic materials and halogencontaining polymers by mixing with the polymer or copolymerizationtherewith.

Compounding, or mixing, of materials with the polymers can generally bethe simplest method. However, the flame retardant additives do notgenerally form chemical bonds with the organic polymer and consequentlyact primarily as fillers with the corresponding dilution or sacrifice ofthe polymer's physical properties.

Copolymerization of the flame retardant materials with the organicmonomers, on the other hand, can provide the advantage expected ofpolymerizable monomers which become chemically bound into the polymerchain itself. Thus, it can be possible that the physical properties ofthe resulting polymer are actually improved while obtaining thebeneficial flame retardancy.

Many bromine containing compounds are known to be useful as flameretardants. As addivitives they are useful to render polymers lessflammable. Polymers have also been made less flammable by halogenincorporation into the polymer by copolymerization with halogencontaining monomers. Examples of such monomers are chloro andbromostyrenes. The latter can be prepared by brominating polystyrene andthen thermally decomposing polybromostyrene into its monomer. Thismonomer in turn can be copolymerized with other monomers to produce anon-flammable polymer with the desired physical properties. However, theyield for the depolymerization reaction is low, and produces otherfragments besides the desired monomer.

This invention circumvents this problem by providing a bromopolymerwhich, it has been discovered, can be decomposed in good yield into itsmonomeric form.

In accordance with this invention, α-methyl-p-bromo-styrene is providedas a flame retardant monomer as well as a unique method for itspreparation and various copolymers thereof.

In the practice of this invention, α-methyl-p-bromo-styrene is preparedby the method which comprises the manipulative steps of brominatingpoly(α-methyl-styrene) and subsequently depolymerizing the brominatedpolymer. In particular, the method comprises obtaining an organicsolvent solution of poly(α-methyl-styrene) having a molecular weight inthe range of about 1000 to about 200,000 and brominating said polymer ata temperature in the range of about 20° C. to about 100° C. with liquidor gaseous bromine and subsequently depolymerizing said brominatedpolymer while essentially simultaneously recovering the product as adistillate by heating said solution to a temperature in the range ofabout 250° C. to about 500° C. preferably about 300° C. to about 400° C.Generally a reduced pressure of about 1 to about 500, preferably about 5to about 200, millimeters of mercury is used. Preferably, thedepolymerization step is conducted by essentially instantaneouslyheating said polymer solution to the required temperature over a periodof about 0.1 second to about 2 minutes.

The depolymerized polymer can be refined by distillation to atemperature of about 60° C. to about 90° C. at a reduced pressure ofabout 0.1 to about 500, preferably about 5 to about 200, millimeters ofmercury to provide a distillate having a melting point of about 12° C.to about 18° C. as determined by heating in a capillary tube at about 1°C. per minute. The distillate is typically further characterized by aboiling point of about 80° C. to about 85° C., at about 7 millimeters ofmercury, a density of about 1.34 to about 1.35 at 25° C. and arefractive index of about 1.579 to about 1.580 at 25° C.

Generally, it is desired to mix with the depolymerized brominatedpolymer a weak base, such as aluminum oxide or magnesium oxide to simplyscavenge or destroy possible residual Lewis acids which might have beenused to prepare the original polymer which could potentiallyrepolymerize the new monomer cationically during the fractionationrecovery step.

The α-methyl-p-bromo-styrene monomer of this invention can be used toenhance flame retardancy of various polymers by free radical additionsolution or emulsion polymerization with various vinyl polymerizabledouble bond compounds. Such reactions are generally conducted with theaid of well-known free radical initiators such as the various peroxides,hydroperoxides, azo compounds as well as redox systems for emulsionpolymerizations. Representative of the many and various vinylpolymerizable double bond compounds are dienes containing 4 to 6 carbonatoms such as 1,3-butadiene, isoprene, dimethyl butadiene andpiperylene; monoolefins containing 2 to 4 carbon atoms such as ethylene,propylene and isobutylene; vinyl aromatic compounds such as styrene,chlorostyrene, vinyl toluene, α-methyl styrene are divinyl benzene;monobasic acid esters such as alkyl (C₁ to C₁₀) and alkoxy (C₁ -C₄)acrylates and methacrylates, especially methyl methacrylate; dibasicacid esters such as maleate, fumarate and itaconate; vinyl cyanides suchas acrylonitrile and methacrylonitrile; vinyl chloride; vinylidenechloride; vinyl ethers such as methyl vinyl ether; vinyl esters such asvinyl acetate and esters of C₈ -C₁₀ acids; vinyl phosphonates;organophosphates such as mono, di and tri allyl phosphates; vinylsilanes; and vinyl antimonies such as antimony fumarate. Particularlyexemplary of aqueous emulsion polymerization systems arebutadiene/styrene and styrene/acrylonitrile copolymer systems.

Generally, it is preferred that such polymers contain and are preparedby copolymerizing the α-methyl-p-bromo-styrene of this invention in anamount in the range of about 5 to about 20 weight percent and, morepreferably, about 10 to about 20 weight percent of the totalpolymerization monomers. However, with regard to copolymerizing withmonomers containing phosphite or antimony, it is understood that therecan be a synergistic effect resulting therefrom and that less amounts ofthe α-methyl-p-bromo-styrene is needed to impart a satisfactory fireretardancy. In such cases, generally about 5 to about 15 or about 20weight percent is satisfactory.

For example, in an aqueous emulsion polymerization situation, it maygenerally be desirable to provide an aqueous emulsion system whichcomprises on a monomer basis about 1 to about 50 weight percentα-methyl-p-bromo-styrene, about 1 to about 40 weight percent styrene andabout 30 to about 90 weight percent butadiene or acrylonitrile, wherethe weight ratio of butadiene to acrylonitrile or styrene is in therange of about 1/1 to about 10/1. The reaction is then continuedaccording to well-known emulsion polymerizing techniques to achieve arubbery material which has improved flame retardancy in accordance withASTM D-635-56T burning test.

The practice of this invention is further illustrated by reference tothe following examples which are intended to be representative ratherthan restrictive of the scope of the invention. Unless otherwiseindicated, all parts and percentages are by weight.

EXAMPLE 1

Poly(α-methyl-styrene) was prepared by first charging to a reactor 2400parts carbon tetrachloride as a solvent and 6 parts ferric chloride as acatalyst into a well stirred flask. The mixture was cooled to about 0°C. and 1180 parts α-methyl-styrene was slowly added thereto on adrop-wise basis and at an even rate over a period of about one hour.After the addition of α-methyl-styrene the reaction temperature wasmaintained at about 0° C. for an additional half hour in order tocomplete the reaction. The poly(α-methyl-styrene) was recovered byfractionation to remove the volatiles therefrom. The non-volatilecontent of the viscous product was found to be about 33 percent of themixture before fractionation which is almost 100 percent of thetheoretical amount obtainable.

The poly(α-methyl-styrene) solution was heated to 55° C. 1760 partsbromine was slowly added drop-wise beneath the surface at a moderaterate, in order to control foaming of the reaction, over a period ofabout 6 hours. During this time, a nitrogen purge was used to facilitatethe removal of hydrogen-bromide which formed by the mixture of thepolymerization reaction. Bromine vapor escape, promoted by the nitrogenpurge was prevented by the use of a dry ice condenser. The mixture wascontained for an additional hour at a temperature in the range of about55° C. about 60° C. in order to complete the reaction.

The resulting poly(α-methyl-p-bromo-styrene) can now be isolated as apolymer or the solution can be used as it is in its present form.Isolation of the polymer in this case was accomplished by precipitatingthe polymer from its carbon tetrachloride solution with methanol, byfiltering and drying the yellowish precipitate. The yield of polymer was1840 parts which amounts to about 94 percent of the amount theoreticallyobtainable.

The polymer was depolymerized by first forming a 50 percent solution ofthe dry polymer with 3900 parts of carbon tetrachloride. The solutionwas slowly added dropwise over a period of about 2 hours to a flaskwhich was a part of a vacuum distillation apparatus. The temperature ofthe flask was adjusted to about 330° C. to about 360° C. at a reducedpressure of about 2 to about 5 millimeters of mercury. Almost instantdepolymerization occurred as each drop was added. At the end of theaddition, about 150 parts of a brittle charred residue remained in theflask. The depolymerized polymer was recovered as the distillate. To thedistillate was added 45 parts magnesium oxide to destroy any residualLewis acid which might repolymerize the newly obtained monomercationically during the ensuing distillation. The distillate was thenredistilled by fractional distillation to obtain a distillate having aboiling point of about 80° C. to about 90° C. at a reduced pressure ofabout 5 to 20 millimeters mercury. The distilled product had thefollowing analysis shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Purity      99-100 percent (by gas chromatography)                            Boiling Point                                                                             81° C. at 7 millimeter mercury pressure                    Density     1.345 at 25° C.                                            Refractive Index                                                                          1.579 at 25° C.                                            Melting Point                                                                             15° C.                                                     ______________________________________                                    

The infrared analysis in combination with the properties shown in Table1 confirmed that the α-methyl-p-bromo-styrene monomer had been obtained.

EXAMPLE II

Aqueous emulsion copolymerizations were conducted with theα-methyl-p-bromo-styrene obtained according to Example I. In one recipe,a 30/35/30 weight ratio ofstyrene/acrylonitrile/α-methyl-p-bromo-styrene monomer system wasemulsion polymerized at a temperature in the range of about 50° to about55° C. In a second recipe, a monomer system comprised 67/33 weightamounts of butadiene/α-methyl-p-bromo-styrene monomer system emulsioncopolymerized at a temperature in the range of about 50° to about 55° C.

The recipe for several aqueous emulsion polymerizations is more clearlyshown in the following Table 2.

                  TABLE 2                                                         ______________________________________                                                      A      B         C                                              ______________________________________                                        Water           165      165       165                                        Emulsifiers     5        5         5                                          Potassium persulfate                                                                          0.5      0.5       0.5                                        Styrene         35       35        25                                         α-methyl-styrene                                                                        35       0         0                                          α-methyl-p-bromo-styrene                                                                0        35        50                                         Acrylonitrile   30       30        25                                         Mercaptan       0.5      0.5       0.5                                        Shortstop       0.05     0.05      0.05                                       Temperature (° F.)                                                                     100      100       100                                        % Solids                                                                      4 hours         2        6.6       15                                         8 hours         5.8      21.6      30.9                                       12 hours        25.6     36.7      34.6                                       16 hours        35.3               36                                         ______________________________________                                    

The resulting emulsion copolymers were tested for flame retardancy andshowed substantially improved results in accordance with ASTM D-635-56T.The favorable flame retardant results are more clearly shown in thefollowing Table 3.

                  TABLE 3                                                         ______________________________________                                        Burn rate    .88"/min self-      self-                                                              extinguishing                                                                            extinguishing                                Seconds burning time                                                          after ignition        13.3       2                                            ______________________________________                                    

Thus, this example demonstrates that the α-methyl-p-bromo-styrenesubstantially enhances the flame retardancy of the styrene/acrylonitrilecopolymer by causing it to be self-extinguishing as compared to simplyusing an α-methyl-styrene which demonstrated a burn rate of 0.88 inchper minute. Furthermore, it should be pointed out that theα-methyl-p-bromo-styrene of this invention demonstrated a more favorableand controllable reaction rate. Namely, the α-methyl-p-bromo-styrenedemonstrated a reaction rate which was controllably faster thanα-methyl-styrene, and therefore a more useful monomer for the purpose ofcopolymerization.

In the practice of this invention, poly(α-methyl-styrene) can bebrominated as a solvent solution, utilizing an inert solvent which isessentially non-reactive in the polymerization system. Particularlypreferred are liquid chlorinated aliphatic hydrocarbons containing 1 to2 carbon atoms. Representative of such chlorinated hydrocarbons arecarbon tetrachloride, chloroform, methylene chloride, dichloro ethane,trichloro ethane and tetrachloro ethane. Generally, carbon tetrachlorideis preferred. In the preparation of the solution, various amounts of theα-methyl-styrene can be used. Generally, a solution containing about 10to about 40 and even up to about 50 weight percent α-methyl-styrene isdesired, depending primarily upon viscosity and solubility limitationsrelating to temperature used and the molecular weight of theα-methyl-styrene itself. In these examples, an α-methyl-styrene having amolecular weight in the range of about 1,000 to about 5,000 was used.

As described in these examples, the α-methyl-p-bromo-styrene can be usedas a co-monomer for enhancing the flame retardancy of copolymers inaccordance with ASTM Test No. D-635-56T. Similarly, theα-methyl-p-bromo-styrene of this invention can be suitably used toenhance the flame retardancy of polymers and copolymers earlierdescribed in this specification through solution and emulsioncopolymerizations.

In the bromination reaction used in this invention, the reaction ratecan be enhanced by conducting the bromination in the presence of a Lewisacid. Representative of the various Lewis acids are ferric chloride,ferric bromide, aluminum chloride, aluminum bromide and zinc chloride.Typically, only very small amounts of such catalysts need to be present,when used, such as from about 0.05 weight percent to about 0.5 or 1weight percent based on the α-methyl-styrene.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed is:
 1. A copolymer of α-methyl-p-bromo-styrene and avinyl polymerizable double bond monomer prepared by free radicaladdition solvent or emulsion copolymerizing a mixture of about 5 toabout 20 weight percent α-methyl-p-bromo-styrene and, correspondingly,about 95 to about 80 weight percent vinyl polymerizable double bondmonomer, where said double bond monomer is selected from at least one ofdienes selected from 1,3-butadiene, isoprene, dimethyl butadiene andpiperylene; monoolefins selected from ethylene, propylene andisobutylene; vinyl aromatic compounds selected from styrene,chlorostyrene, vinyl toluene, α-methyl styrene and divinyl benzene;monobasic acid esters selected from alkyl (C₁ to C₁₀) and alkoxy (C₁-C₄) acrylates and methacrylates; dibasic acid esters selected frommaleate, fumarate and itaconates; vinyl cyanides selected fromacrylonitrile and methacrylonitrile; vinyl chloride, vinylidenechloride; methyl vinyl ether; vinyl esters selected from vinyl acetateand esters of C₈ -C₁₀ acids; vinyl phosphonates; organophosphatesselected from mono-, di- and triallyl phosphates; vinyl silanes;antimony fumarate.
 2. The copolymer of claim 1 where said double bondmonomer is methyl methacrylate.
 3. The copolymer of claim 1 prepared byaqueous emulsion polymerizing α-methyl-p-bromo-styrene with a mixture ofvinyl polymerizable double bond monomers comprised of (1) butadiene and(2) acrylonitrile or styrene, where the weight ratio of butadiene toacrylonitrile or styrene is in the range of about 1/1 to about 10/1. 4.The copolymer of claim 3 where said copolymer is prepared by aqueousemulsion polymerizing a mixture of α-methyl-p-bromo-styrene of claim 7,1,3-butadiene and styrene, where said mixture comprises about 5 to about20 weight percent α-methyl-p-bromo-styrene based on the total monomermixture.